Printhead with columns extending across chamber inlet

ABSTRACT

An inkjet printhead for a printer that prints via an array of ink ejection devices. Each ink ejection device has a chamber for holding a quantity of ink. The chamber is partially defined by at least one sidewall and has an inlet in fluid communication with the chamber. The inlet defines a flow path into the chamber and has a series of columns extending across the flow path. The series of chambers form a barrier structure that creates a flow constriction that traps contaminants in the ink flow.

CROSS REFERENCE TO RELATED APPLICATION

The present application is a continuation of U.S. application Ser No.11/926,109 filed Oct. 28, 2007, now issued U.S. Pat. No. 7,568,788,which is a continuation of U.S. application Ser. No. 11/778,572 filed onJul. 16, 2007, now issued U.S. Pat. No. 7,566,113, which is acontinuation of U.S. application Ser. No. 11/349,074 filed on Feb. 8,2006, now issued U.S. Pat. No. 7,255,424, which is a continuation ofU.S. application Ser No. 10/982,789 filed on Nov. 8, 2004, now issuedU.S. Pat. No. 7,086,720, which is a continuation of U.S. applicationSer. No. 10/421,823 filed on Apr. 24, 2003, now issued U.S. Pat. No.6,830,316, which is a continuation of U.S. application Ser. No.09/113,122 filed on Jul. 10, 1998, now issued U.S. Pat. No. 6,557,977,all of which are herein incorporated by reference.

CROSS REFERENCES TO RELATED APPLICATIONS

The following U.S. patents and U.S. patent applications are herebyincorporated by cross-reference.

U.S. Pat. No./U.S. patent application Ser. No. Incorporated byReference: Docket No. 6,750,901 ART01US 6,476,863 ART02US 6,788,336ART03US 6,322,181 ART04US 6,597,817 ART06US 6,227,648 ART07US 6,727,948ART08US 6,690,419 ART09US 6,727,951 ART10US 6,196,541 ART13US 6,195,150ART15US 6,362,868 ART16US 6,831,681 ART18US 6,431,669 ART19US 6,362,869ART20US 6,472,052 ART21US 6,356,715 ART22US 6,894,694 ART24US 6,636,216ART25US 6,366,693 ART26US 6,329,990 ART27US 6,459,495 ART29US 6,137,500ART30US 6,690,416 ART31US 7,050,143 ART32US 6,398,328 ART33US 7,110,024ART34US 6,431,704 ART38US 6,879,341 ART42US 6,415,054 ART43US 6,665,454ART45US 6,542,645 ART46US 6,486,886 ART47US 6,381,361 ART48US 6,317,192ART50US 6,850,274 ART51US 09/113,054 ART52US 6,646,757 ART53US 6,624,848ART56US 6,357,135 ART57US 6,271,931 ART59US 6,353,772 ART60US 6,106,147ART61US 6,665,008 ART62US 6,304,291 ART63US 6,305,770 ART65US 6,289,262ART66US 6,315,200 ART68US 6,217,165 ART69US 6,786,420 DOT01US 6,350,023FLUID01US 6,318,849 FLUID02US 6,227,652 IJ01US 6,213,588 IJ02US6,213,589 IJ03US 6,231,163 IJ04US 6,247,795 IJ05US 6,394,581 IJ06US6,244,691 IJ07US 6,257,704 IJ08US 6,416,168 IJ09US 6,220,694 IJ10US6,257,705 IJ11US 6,247,794 IJ12US 6,234,610 IJ13US 6,247,793 IJ14US6,264,306 IJ15US 6,241,342 IJ16US 6,247,792 IJ17US 6,264,307 IJ18US6,254,220 IJ19US 6,234,611 IJ20US 6,302,528 IJ21US 6,283,582 IJ22US6,239,821 IJ23US 6,338,547 IJ24US 6,247,796 IJ25US 6,557,977 IJ26US6,390,603 IJ27US 6,362,843 IJ28US 6,293,653 IJ29US 6,312,107 IJ30US6,227,653 IJ31US 6,234,609 IJ32US 6,238,040 IJ33US 6,188,415 IJ34US6,227,654 IJ35US 6,209,989 IJ36US 6,247,791 IJ37US 6,336,710 IJ38US6,217,153 IJ39US 6,416,167 IJ40US 6,243,113 IJ41US 6,283,581 IJ42US6,247,790 IJ43US 6,260,953 IJ44US 6,267,469 IJ45US 6,224,780 IJM01US6,235,212 IJM02US 6,280,643 IJM03US 6,284,147 IJM04US 6,214,244 IJM05US6,071,750 IJM06US 6,267,905 IJM07US 6,251,298 IJM08US 6,258,285 IJM09US6,225,138 IJM10US 6,241,904 IJM11US 6,299,786 IJM12US 6,866,789 IJM13US6,231,773 IJM14US 6,190,931 IJM15US 6,248,249 IJM16US 6,290,862 IJM17US6,241,906 IJM18US 6,565,762 IJM19US 6,241,905 IJM20US 6,451,216 IJM21US6,231,772 IJM22US 6,274,056 IJM23US 6,290,861 IJM24US 6,248,248 IJM25US6,306,671 IJM26US 6,331,258 IJM27US 6,110,754 IJM28US 6,294,101 IJM29US6,416,679 IJM30US 6,264,849 IJM31US 6,254,793 IJM32US 6,235,211 IJM35US6,491,833 IJM36US 6,264,850 IJM37US 6,258,284 IJM38US 6,312,615 IJM39US6,228,668 IJM40US 6,180,427 IJM41US 6,171,875 IJM42US 6,267,904 IJM43US6,245,247 IJM44US 6,315,914 IJM45US 6,231,148 IR01US 6,293,658 IR04US6,614,560 IR05US 6,238,033 IR06US 6,312,070 IR10US 6,238,111 IR12US6,378,970 IR16US 6,196,739 IR17US 6,270,182 IR19US 6,152,619 IR20US6,087,638 MEMS02US 6,340,222 MEMS03US 6,041,600 MEMS05US 6,299,300MEMS06US 6,067,797 MEMS07US 6,286,935 MEMS09US 6,044,646 MEMS10US6,382,769 MEMS13US

FIELD OF THE INVENTION

This invention relates to the use of a shape memory alloy in amicro-electromechanical fluid ejection device.

The present invention also relates to ink jet printing and in particulardiscloses a shape memory alloy ink jet printer.

The present invention further relates to the field of drop on demand inkjet printing.

BACKGROUND OF THE INVENTION

Many different types of printing have been invented, a large number ofwhich are presently in use. The known forms of print have a variety ofmethods for marking the print media with a relevant marking media.Commonly used forms of printing include offset printing, laser printingand copying devices, dot matrix type impact printers, thermal paperprinters, film recorders, thermal wax printers, dye sublimation printersand ink jet printers both of the drop on demand and continuous flowtype. Each type of printer has its own advantages and problems whenconsidering cost, speed, quality, reliability, simplicity ofconstruction and operation etc.

In recent years, the field of ink jet printing, wherein each individualpixel of ink is derived from one or more ink nozzles has becomeincreasingly popular primarily due to its inexpensive and versatilenature.

Many different techniques on ink jet printing have been invented. For asurvey of the field, reference is made to an article by J Moore,“Non-Impact Printing: Introduction and Historical Perspective”, OutputHard Copy Devices, Editors R Dubeck and S Sherr, pages 207-220 (1988).

Ink Jet printers themselves come in many different types. Theutilisation of a continuous stream ink in ink jet printing appears todate back to at least 1929 wherein U.S. Pat. No. 1,941,001 by Hanselldiscloses a simple form of continuous stream electro-static ink jetprinting.

U.S. Pat. No. 3,596,275 by Sweet also discloses a process of acontinuous ink jet printing including the step wherein the ink jetstream is modulated by a high frequency electro-static field so as tocause drop separation. This technique is still utilized by severalmanufacturers including Elmjet and Scitex (see also U.S. Pat. No.3,373,437 by Sweet et al)

Piezoelectric ink jet printers are also one form of commonly utilizedink jet printing device. Piezoelectric systems are disclosed by Kyseret. al. in U.S. Pat. No. 3,946,398 (1970) which utilizes a diaphragmmode of operation, by Zolten in U.S. Pat. No. 3,683,212 (1970) whichdiscloses a squeeze mode of operation of a piezoelectric crystal, Stemmein U.S. Pat. No. 3,747,120 (1972) discloses a bend mode of piezoelectricoperation, Howkins in U.S. Pat. No. 4,459,601 discloses a piezoelectricpush mode actuation of the ink jet stream and Fischbeck in U.S. Pat. No.4,584,590 which discloses a shear mode type of piezoelectric transducerelement.

Recently, thermal ink jet printing has become an extremely popular formof ink jet printing. The ink jet printing techniques include thosedisclosed by Endo et al in GB 2007162 (1979) and Vaught et al in U.S.Pat. No. 4,490,728. Both the aforementioned references disclosed ink jetprinting techniques rely upon the activation of an electrothermalactuator which results in the creation of a bubble in a constrictedspace, such as a nozzle, which thereby causes the ejection of ink froman aperture connected to the confined space onto a relevant print media.Manufacturers such as Canon and Hewlett Packard manufacture printingdevices utilizing the electro-thermal actuator.

As can be seen from the foregoing, many different types of printingtechnologies are available. Ideally, a printing technology should have anumber of desirable attributes. These include inexpensive constructionand operation, high-speed operation, safe and continuous long-termoperation etc. Each technology may have its own advantages anddisadvantages in the areas of cost, speed, quality, reliability, powerusage, simplicity of construction operation, durability and consumables.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an alternativearrangement of a buckle/diaphragm actuated ink jet print head, simpleand compact in construction however, allowing for a higher speedoperation of the ink jet head through the utilization of substantiallyless energy per ink drop ejected.

It is another object to provide for a new form of ink jet printingdevice that utilizes a shape memory alloy in its activation method.

According to a first aspect of the invention, there is provided aprinthead for an inkjet printer, the printhead comprising:

an array of ink ejection devices, each ink ejection device having achamber for holding a quantity of ink, an inlet in fluid communicationwith the chamber, an actuator disposed in the chambers respectively, anozzle aperture in fluid communication with each of the chambersrespectively; wherein,

the inlet defines a flow path into the chamber and has a barrierstructure extending through the flow path.

Preferably, the barrier structure has column features extending throughthe flow path.

Preferably the column features are integrally formed with one side ofthe inlet.

Preferably the nozzle is formed in a nozzle plate on the printheadexterior, and the column features are integrally formed with the nozzleplate.

Preferably the actuator is configured to displace a surface within thechamber to eject ink from the nozzle.

Preferably the actuator has a heater element for displacing the surfaceusing thermal expansion.

Preferably the surface is positioned in the chamber such that it opposesthe nozzle and the flow path from the inlet feeds ink between the nozzleand the surface of the actuator.

Preferably the surface defines a wall of the chamber opposite thenozzle.

Preferably the surface is formed from material includingpolytetrafluoroethylene.

Preferably, during use, the surface reduces the chamber volume to ejectink from the nozzle.

Preferably, during use, the surface increases the chamber volume as theactuator returns to its quiescent position after ejecting ink in orderto draw refill ink through the barrier structure in the inlet.

Preferably the surface has a quadrilateral geometry and is fixed at twoopposing parallel sides such that the surface buckles into the chamberwhen during actuation, and flattens when returning to its quiescentstate.

Preferably the heater element is a conductor with a serpentine geometryextending across most of the surface.

Preferably, the printhead further comprising an air space on non-inkcontacting side of the surface.

Preferably the air space is vented to atmosphere.

Preferably the non-ink contacting side of the surface is hydrophobic formaintaining the air space.

Preferably the barrier structure creates a flow restriction for therefill ink flow to damp oscillations in ink in the chamber immediatelyafter refill.

Preferably the barrier structure in a grille for filtering contaminantsout of the ink flow into the chamber.

In another aspect, the invention provides a micro-electromechanicalfluid ejection device which comprises

a wafer substrate;

drive circuitry positioned on the wafer substrate;

a nozzle chamber structure arranged on the wafer substrate to define anozzle chamber and a fluid ejection port in fluid communication with thenozzle chamber; and

a fluid ejection member that is operatively positioned with respect tothe nozzle chamber such that displacement of the fluid ejection memberresults in the ejection of fluid from the fluid ejection port, wherein

at least a portion of the fluid ejection member is of a shape memoryalloy which defines an electrical heating circuit and which is connectedto the drive circuitry to be heated by an electrical current receivedfrom the drive circuitry, the shape memory alloy being displaceabletowards the fluid ejection port when heated to transform from itsmartensitic phase to its austenitic phase to eject fluid from the fluidejection port.

The nozzle chamber structure may be defined partly by the substratewhich is etched to define walls of the nozzle chamber. The substrate mayinclude a structural layer which is etched to define the fluid ejectionport.

The heating circuit defined by the shape memory alloy may be interposedbetween a pair of structural layers. One of the structural layers may bepre-stressed so that, upon release, the fluid ejection member is drawnaway from the fluid ejection port while the shape memory alloy is in themartensitic phase.

The structural layers may be of a resiliently flexible material which isconfigured so that the shape memory alloy can be drawn away from thefluid ejection port when the heating circuit cools and the alloy becomesmartensitic.

The heating circuit defined by the shape memory alloy may trace aserpentine path from one via to another, the via providing an electricalconnection to the heating circuit.

The nozzle chamber may be in fluid communication with a fluid reservoir.One of the structural layers may form part of a fluid passivation layerthat covers the drive circuitry layer to protect the drive circuitrylayer from fluid damage.

In accordance with a second aspect of the present invention there isprovided a method of ejecting ink from a chamber comprising the stepsof: a) providing a cantilevered beam actuator incorporating a shapememory alloy; and b) transforming said shape memory alloy from itsmartensitic phase to its austenitic phase or vice versa to cause the inkto eject from said chamber. Further, the actuator comprises a conductiveshape memory alloy panel in a quiescent state and which transfers to anink ejection state upon heating thereby causing said ink ejection fromthe chamber. Preferably, the heating occurs by means of passing acurrent through the shape memory alloy. The chamber is formed from acrystallographic etch of a silicon wafer so as to have one surface ofthe chamber substantially formed by the actuator. Advantageously, theactuator is formed from a conductive shape memory alloy arranged in aserpentine form and is attached to one wall of the chamber opposite anozzle port from which ink is ejected. Further, the back etching of asilicon wafer to the epitaxial layer and etching a nozzle porthole inthe epitaxial layer forms the nozzle port. The crystallographic etchincludes providing side wall slots of non-etched layers of a processedsilicon wafer so as to extend the dimensions of the chamber as a resultof the crystallographic etch process. Preferably, the shape memory alloycomprises nickel titanium alloy.

By way of background, reference is made to U.S. patent application Ser.No. 09/113,097 by the applicant. It is an object of the invention ofthat application to provide an alternative form of drop on demand inkjet printing utilising a reverse spring lever arrangement to actuate theejection of ink from a nozzle chamber.

In accordance with a third aspect of that invention, there is providedan ink jet printing nozzle apparatus with a connected ink supplychamber, the apparatus comprising an ink ejection means having onesurface in fluid communication with the ink in the nozzle chamber, arecoil means connected to the ink ejection means and a first actuatormeans connected to the ink ejection means. The method of ejecting inkfrom the ink chamber comprises the steps of activation of the firstactuator means which drives the ink ejection means from a quiescentposition to a pre-firing position and deactivation of the first actuatormeans, causing the recoil means to drive the ink ejection means to ejectink from the nozzle chamber through the ink ejection port. Further, therecoil means includes a resilient member and the movement of the firstactuator results in resilient movement of this recoil means and thedriving of the ink ejection means comprises the resilient member actingupon the ink ejection means. Preferably, the first actuator meanscomprises an electromagnetic actuator and the recoil means comprises atorsional spring. The ink ejection means and the first actuator areinterconnected in a cantilever arrangement wherein small movements ofthe first actuator means result in larger movements of the ink ejectionmeans. Advantageously, the recoil means is located substantially at thepivot point of the cantilever construction. The first actuator includesa solenoid coil surrounded by a magnetic actuator having a first mixedmagnetic pole and a second moveable magnetic pole, such that, uponactivation of the coil, the poles undergo movement relative to oneanother with the moveable magnetic pole being connected to the actuatorside of the cantilever construction. Preferably, the moveable magneticpole includes a plurality of slots for the flow of ink through the poleupon movement. The ink ejection means comprises a piston or plungerhaving a surface substantially mating with at least one surface of thenozzle chamber.

Also by way of background, reference is made to U.S. patent applicationSer. No. 09/113,061 by the applicant. It is an object of the inventionof that application to provide for an alternative form of ink jetprinter which uses a linear stepper actuator to eject ink from a nozzlechamber.

In accordance with a fourth aspect of that invention, an ink jet nozzlearrangement is presented comprising: a nozzle chamber having an inkejection port for the ejection of ink, an ink supply reservoir forsupplying ink to the nozzle chamber, a plunger located within the nozzlechamber and further, a linear stepper actuator interconnected to theplunger and adapted to actuate the plunger so as to cause the ejectionof ink from the ink ejection port. At least one surface of the plungerlocated alongside a wall of the nozzle chamber is hydrophobic.Preferably, the linear actuator interconnected to the plunger in thenozzle chamber is driven in three phases by a series of electromagnets.Preferably, a series of twelve electromagnets is arranged in opposingpairs alongside the linear actuator. Further, each phase is duplicatedresulting in four electromagnets for each phase. The ink jet nozzle hasan open wall along a back surface of the plunger which comprises aseries of posts adapted to form a filter to filter ink flowing throughthe open wall into the nozzle chamber. The linear actuator constructionincludes a guide at the end opposite to the nozzle chamber for guidingthe linear actuator.

BRIEF DESCRIPTION OF THE DRAWINGS

Notwithstanding any other forms which may fall within the scope of thepresent invention, preferred forms of the invention will now bedescribed, by way of example only, with reference to the accompanyingdrawings in which:

FIG. 1 is an exploded, perspective view of a single ink jet nozzle asconstructed in accordance with the preferred embodiment of theinvention;

FIG. 2 is a cross-sectional view of a single ink jet nozzle in itsquiescent state taken along line A-A in FIG. 1;

FIG. 3 is a top cross sectional view of a single ink jet nozzle in itsactuated state taken along line A-A in FIG. 1;

FIG. 4 provides a legend of the materials indicated in FIG. 5 to 15;

FIG. 5 to FIG. 15 illustrate sectional views of the manufacturing stepsin one form of construction of an ink jet printhead nozzle;

FIG. 16 is an exploded perspective view illustrating the construction ofa single ink jet nozzle of U.S. patent application Ser. No. 09/113,097by the Applicant, referred to in the table of cross-referenced materialas set out above;

FIG. 17 is a perspective view, in part in section, of the ink jet nozzleof FIG. 16;

FIG. 18 provides a legend of the materials indicated in FIGS. 19 to 35;

FIGS. 19 to 35 illustrate sectional views of the manufacturing steps inone form of construction of the ink jet printhead nozzle of FIG. 16;

FIG. 36 is a cut-out top view of an ink jet nozzle of U.S. patentapplication Ser. No. 09/113,061 by the Applicant, referred to in thetable of cross-referenced material as set out above;

FIG. 37 is an exploded perspective view illustrating the construction ofthe ink jet nozzle of FIG. 36;

FIG. 38 provides a legend of the materials indicated in FIGS. 39 to 59;

FIGS. 39 to 59 illustrate sectional views of the manufacturing steps inone form of construction of the ink jet printhead nozzle of FIG. 36;

FIG. 60 is a perspective view partly in sections of a single ink jetnozzle constructed in accordance with the preferred embodiment;

FIG. 61 is an exploded perspective view partly in section illustratingthe construction of a single ink nozzle in accordance with the preferredembodiment of the present invention;

FIG. 62 provides a legend of the materials indicated in FIG. 63 to 75;and,

FIGS. 63 to 75 illustrate sectional views of the manufacturing steps inone form of construction of an ink jet printhead nozzle.

DESCRIPTION OF PREFERRED AND OTHER EMBODIMENTS

In the preferred embodiment, shape memory materials are utilised toconstruct an actuator suitable for injecting ink from the nozzle of anink chamber.

Turning to FIG. 1, there is illustrated an exploded perspective view 10of a single ink jet nozzle as constructed in accordance with thepreferred embodiment. The ink jet nozzle 10 is constructed from asilicon wafer base utilizing back etching of the wafer to a boron dopedepitaxial layer. Hence, the ink jet nozzle 10 comprises a lower layer 11which is constructed from boron-doped silicon. The boron doped siliconlayer is also utilized as a crystallographic etch stop layer. The nextlayer comprises the silicon layer 12 that includes a crystallographicpit that defines a nozzle chamber 13 having side walls etched at theconventional angle of 54.74 degrees. The layer 12 also includes thevarious required circuitry and transistors for example, a CMOS layer(not shown). After this, a 0.5-micron thick thermal silicon oxide layer15 is grown on top of the silicon wafer 12.

After this, come various layers which can comprise two-level metal CMOSprocess layers which provide the metal interconnect for the CMOStransistors formed within the layer 12. The various metal pathways etc.are not shown in FIG. 1 but for two metal interconnects 18, 19 whichprovide interconnection between a shape memory alloy layer 20 and theCMOS metal layers 16. The shape memory metal layer is next and is shapedin the form of a serpentine coil to be heated by end interconnect/viaportions 21,23. A top nitride layer 22 is provided for overallpassivation and protection of lower layers in addition to providing ameans of inducing tensile stress to curl the shape memory alloy layer 20in its quiescent state.

The preferred embodiment relies upon the thermal transition of a shapememory alloy 20 (SMA) from its martensitic phase to its austeniticphase. The basis of a shape memory effect is a martensitictransformation from a thermoelastic martensite at a relatively lowtemperature to an austenite at a higher temperature. The thermaltransition is achieved by passing an electrical current through the SMA.The layer 20 is suspended at the entrance to a nozzle chamber connectedvia leads 18, 19 to the layers 16.

In FIG. 2, there is shown a cross-section of a single nozzle 10 when inits quiescent state, the section being taken through the line A-A ofFIG. 1. An actuator 30 that includes the layers 20, 22, is bent awayfrom a nozzle port 47 when in its quiescent state. In FIG. 3, there isshown a corresponding cross-section for the nozzle 10 when in anactuated state. When energized, the actuator 30 straightens, with thecorresponding result that the ink is pushed out of the nozzle. Theprocess of energizing the actuator 30 requires supplying enough energyto raise the SMA layer 20 above its transition temperature so that theSMA layer 20 moves as it is transformed into its austenitic phase.

The SMA martensitic phase must be pre-stressed to achieve a differentshape from the austenitic phase. For printheads with many thousands ofnozzles, it is important to achieve this pre-stressing in a bulk manner.This is achieved by depositing the layer of silicon nitride 22 usingPlasma Enhanced Chemical Vapour Deposition (PECVD) at around 300° C.over the SMA layer. The deposition occurs while the SMA is in theaustenitic shape. After the printhead cools to room temperature thesubstrate under the SMA bend actuator is removed by chemical etching ofa sacrificial substance. The silicon nitride layer 22 is thus placedunder tensile stress and curls away from the nozzle port 47. The weakmartensitic phase of the SMA provides little resistance to this curl.When the SMA is heated to its austenitic phase, it returns to the flatshape into which it was annealed during the nitride deposition. Thetransformation is rapid enough to result in the ejection of ink from thenozzle chamber.

There is one SMA bend actuator 30 for each nozzle. One end 31 of the SMAbend actuator 30 is mechanically connected to the substrate. The otherend is free to move under the stresses inherent in the layers.

Returning to FIG. 1, the actuator layer is composed of three layers:

1. The SiO₂ lower layer 15. This layer acts as a stress ‘reference’ forthe nitride tensile layer. It also protects the SMA from thecrystallographic silicon etch that forms the nozzle chamber. This layercan be formed as part of the standard CMOS process for the activeelectronics of the printhead.

2. An SMA heater layer 20. An SMA such as a nickel titanium (NiTi) alloyis deposited and etched into a serpentine form to increase theelectrical resistance so that the SMA is heated when an electricalcurrent is passed through the SMA.

3. A silicon nitride top layer 22. This is a thin layer of highstiffness which is deposited using PECVD. The nitride stoichiometry isadjusted to achieve a layer with significant tensile stress at roomtemperature relative to the SiO₂ lower layer. Its purpose is to bend theactuator at the low temperature martensitic phase, away from the nozzleport 47.

As noted previously, the ink jet nozzle of FIG. 1 can be constructed byutilizing a silicon wafer having a buried boron epitaxial layer. The 0.5micron thick dioxide layer 15 is then formed having side slots 45 whichare utilized in a subsequent crystallographic etch. Next, the variousCMOS layers 16 are formed including drive and control circuitry (notshown). The SMA layer 20 is then created on top of layers 15/16 and isconnected with the drive circuitry. The silicon nitride layer 22 is thenformed on the layer 20. Each of the layers 15, 16, 22 includes thevarious slots 45 which are utilized in a subsequent crystallographicetch. The silicon wafer is subsequently thinned by means of back etchingwith the etch stop being the boron-doped silicon layer 11. Subsequentetching of the layer 11 forms the nozzle port 47 and a nozzle rim 46. Anozzle chamber is formed by means of a crystallographic etch with theslots 45 defining the extent of the etch within the silicon oxide layer12.

A large array of nozzles can be formed on the same wafer which in turnis attached to an ink chamber for filling the nozzle chambers.

One form of detailed manufacturing process which can be used tofabricate monolithic ink jet printheads operating in accordance with theprinciples taught by the present embodiment can proceed utilizing thefollowing steps:

1. Using a double-sided polished wafer 50, deposit 3 microns ofepitaxial silicon 11 heavily doped with boron.

2. Deposit 10 microns of epitaxial silicon 12, either p-type or n-type,depending on the CMOS process used.

3. Complete drive transistors, data distribution, and timing circuitsusing a 0.5-micron, one poly, 2 metal CMOS process to define the CMOSmetal layers 16. This step is shown in FIG. 5. For clarity, thesediagrams may not be to scale, and may not represent a cross sectionthough any single plane of the nozzle. FIG. 4 is a key torepresentations of various materials in these manufacturing diagrams,and those of other cross-referenced ink jet configurations.

4. Etch the CMOS oxide layers down to silicon or aluminum using Mask 1.This mask defines the nozzle chamber, and the edges of the printheadschips. This step is shown in FIG. 6.

5. Crystallographically etch the exposed silicon using, for example, KOHor EDP (ethylenediamine pyrocatechol). This etch stops on <111>crystallographic planes 51, and on the boron doped silicon buried layer.This step is shown in FIG. 7.

6. Deposit 12 microns of sacrificial material 52. Planarize down tooxide using CMP. The sacrificial material 52 temporarily fills thenozzle cavity. This step is shown in FIG. 8.

7. Deposit 0.1 microns of high stress silicon nitride (Si3N4) 53.

8. Etch the nitride layer 53 using Mask 2. This mask defines the contactvias from the shape memory heater to the second-level metal contacts.

9. Deposit a seed layer.

10. Spin on 2 microns of resist, expose with Mask 3, and develop. Thismask defines the shape memory wire embedded in the paddle. The resistacts as an electroplating mold. This step is shown in FIG. 9.

11. Electroplate 1 micron of Nitinol 55 on the sacrificial material 52to fill the electroplating mold. Nitinol is a ‘shape memory’ alloy ofnickel and titanium, developed at the Naval Ordnance Laboratory in theUS (hence Ni-Ti-NOL). A shape memory alloy can be thermally switchedbetween its weak martensitic state and its high stiffness austeniticstate.

12. Strip the resist and etch the exposed seed layer. This step is shownin FIG. 10.

13. Wafer probe. All electrical connections are complete at this point,bond pads are accessible, and the chips are not yet separated.

14. Deposit 0.1 microns of high stress silicon nitride. High stressnitride is used so that once the sacrificial material is etched, and thepaddle is released, the stress in the nitride layer will bend therelatively weak martensitic phase of the shape memory alloy. As theshape memory alloy, in its austenitic phase, is flat when it is annealedby the relatively high temperature deposition of this silicon nitridelayer, it will return to this flat state when electrothermally heated.

15. Mount the wafer 50 on a glass blank 56 and back-etch the wafer usingKOH with no mask. This etch thins the wafer and stops at the buriedboron doped silicon layer. This step is shown in FIG. 11.

16. Plasma back-etch the boron doped silicon layer to a depth of 1micron using Mask 4. This mask defines the nozzle rim 46. This step isshown in FIG. 12.

17. Plasma back-etch through the boron doped layer using Mask 5. Thismask defines the nozzle port 47, and the edge of the chips. At thisstage, the chips are still mounted on the glass blank 56. This step isshown in FIG. 13.

18. Strip the adhesive layer to detach the chips from the glass blank.Etch the sacrificial layer 52 away. This process completely separatesthe chips. This step is shown in FIG. 14.

19. Mount the printheads in their packaging, which may be a moldedplastic former incorporating ink channels which supply different colorsof ink to the appropriate regions of the front surface of the wafer.

20. Connect the printheads to their interconnect systems.

21. Hydrophobize the front surface of the printheads.

22. Fill with ink and test the completed printheads. A filled nozzle isshown in FIG. 15.

An embodiment of U.S. patent application Ser. No. 09/113,097 by theapplicant is now described. This embodiment relies upon a magneticactuator to “load” a spring, such that, upon deactivation of themagnetic actuator the resultant movement of the spring causes ejectionof a drop of ink as the spring returns to its original position.

In FIG. 16, there is illustrated an exploded perspective view of an inknozzle arrangement 60 constructed in accordance with the preferredembodiment. It would be understood that the preferred embodiment can beconstructed as an array of nozzle arrangements 60 so as to together forman array for printing.

The operation of the ink nozzle arrangement 60 of FIG. 16 proceeds by asolenoid 62 being energized by way of a driving circuit 64 when it isdesired to print out an ink drop. The energized solenoid 62 induces amagnetic field in a fixed soft magnetic pole 66 and a moveable softmagnetic pole 68. The solenoid power is turned on to a maximum currentfor long enough to move the moveable pole 68 from its rest position to astopped position close to the fixed magnetic pole 66. The ink nozzlearrangement 60 of FIG. 1 sits within an ink chamber filled with ink.Therefore, holes 70 are provided in the moveable soft magnetic pole 68for “squirting” out of ink from around the solenoid 62 when the pole 66undergoes movement.

A fulcrum 72 with a piston head 74 balances the moveable soft magneticpole 66. Movement of the magnetic pole 66 closer to the fixed pole 66causes the piston head 74 to move away from a nozzle chamber 76 drawingair into the chamber 76 via an ink ejection port 78. The piston head 74is then held open above the nozzle chamber 76 by means of maintaining alow “keeper” current through the solenoid 62. The keeper level currentthrough solenoid 62 is sufficient to maintain the moveable pole 68against the fixed soft magnetic pole 66. The level of current will besubstantially less than the maximum current level because a gap 114(FIG. 35) between the two poles 66 and 68 is at a minimum. For example,a keeper level current of 10% of the maximum current level may besuitable. During this phase of operation, the meniscus of ink at thenozzle tip or ink ejection port 78 is a concave hemisphere due to theinflow of air. The surface tension on the meniscus exerts a net force onthe ink which results in ink flow from an ink chamber into the nozzlechamber 76. This results in the nozzle chamber 76 refilling, replacingthe volume taken up by the piston head 74 which has been withdrawn. Thisprocess takes approximately 100 μs.

The current within solenoid 62 is then reversed to half that of themaximum current. The reversal demagnetises the magnetic poles 66, 68 andinitiates a return of the piston 74 to its rest position. The piston 74is moved to its normal rest position by both magnetic repulsion and byenergy stored in a stressed torsional spring 80, 82 which was put in astate of torsion upon the movement of moveable pole 68.

The forces applied to the piston 74 as a result of the reverse currentand spring 80, 82 is greatest at the beginning of the movement of thepiston 74 and decreases as the spring elastic stress falls to zero. As aresult, the acceleration of piston 74 is high at the beginning of areverse stroke and the resultant ink velocity within the nozzle chamber76 becomes uniform during the stroke. This results in an increasedoperating tolerance before ink flow over the printhead surface occurs.

At a predetermined time during the return stroke, the solenoid reversecurrent is turned off. The current is turned off when the residualmagnetism of the movable pole is at a minimum. The piston 74 continuesto move towards its original rest position.

The piston 74 overshoots the quiescent or rest position due to itsinertia. Overshoot in the piston movement achieves two things: greaterejected drop volume and velocity, and improved drop break off as thepiston 74 returns from overshoot to its quiescent position.

The piston 74 eventually returns from overshoot to the quiescentposition. This return is caused by the springs 80, 82 which are nowstressed in the opposite direction. The piston return “sucks” some ofthe ink back into the nozzle chamber 76, causing the ink ligamentconnecting the ink drop to the ink in the nozzle chamber 76 to thin. Theforward velocity of the drop and the backward velocity of the ink in thenozzle chamber 76 are resolved by the ink drop breaking off from the inkin the nozzle chamber 76.

The piston 74 stays in the quiescent position until the next dropejection cycle.

A liquid ink printhead has one ink nozzle arrangement 60 associated witheach of the multitude of nozzles. The arrangement 60 has the followingmajor parts:

(1) Drive circuitry 64 for driving the solenoid 62.

(2) The ejection port 78. The radius of the ejection port 78 is animportant determinant of drop velocity and drop size.

(3) The piston 74. This is a cylinder which moves through the nozzlechamber 76 to expel the ink. The piston 74 is connected to one end of alever arm 84. The piston radius is approximately 1.5 to 2 times theradius of the ejection port 78. The volume of ink displaced by thepiston 74 during the piston return stroke mostly determines the ink dropvolume output.

(4) The nozzle chamber 76. The nozzle chamber 76 is slightly wider thanthe piston 74. The gap 114 (FIGS. 34 & 35) between the piston 74 and thenozzle chamber walls is as small as is required to ensure that thepiston does not make contact with the nozzle chamber 76 during actuationor return. If the printheads are fabricated using 0.5 μm semiconductorlithography, then a 1 μm gap 114 will usually be sufficient. The nozzlechamber 76 is also deep enough so that air ingested through the ejectionport 78 when the piston 74 returns to its quiescent state does notextend to the piston 74. If it does, the ingested bubble may form acylindrical surface instead of a hemispherical surface. If this happens,the nozzle will not refill properly.

(5) The solenoid 62. This is a spiral coil of copper. Copper is used forits low resistivity and high electro-migration resistance.

(6) The fixed magnetic pole 66 of ferromagnetic material.

(7) The moveable magnetic pole 68 of ferromagnetic material. To maximisethe magnetic force generated, the moveable magnetic pole 68 and fixedmagnetic pole 66 surround the solenoid 62 to define a torus. Thus,little magnetic flux is lost, and the flux is concentrated across thegap between the moveable magnetic pole 68 and the fixed pole 66. Themoveable magnetic pole 68 has the holes 70 above the solenoid 62 toallow trapped ink to escape. These holes 70 are arranged and shaped soas to minimise their effect on the magnetic force generated between themoveable magnetic pole 68 and the fixed magnetic pole 66.

(8) The magnetic gap 114. The gap 114 between the fixed pole 66 and themoveable pole 68 is one of the most important “parts” of the printactuator. The size of the gap 114 strongly affects the magnetic forcegenerated, and also limits the travel of the moveable magnetic pole 68.A small gap is desirable to achieve a strong magnetic force. The travelof the piston 74 is related to the travel of the moveable magnetic pole68 (and therefore the gap 114) by the lever arm 84.

(9) Length of the lever arm 84. The lever arm 84 allows the travel ofthe piston 74 and the moveable magnetic pole 68 to be independentlyoptimised. At the short end of the lever arm 84 is the moveable magneticpole 68. At the long end of the lever arm 84 is the piston 74. Thespring 80, 82 is at the fulcrum 72. The optimum travel for the moveablemagnetic pole 68 is less than 1 mm, so as to minimise the magnetic gap.The optimum travel for the piston 74 is approximately 5 μm for a 1200dpi printer. A lever 84 resolves the difference in optimum travel with a5:1 or greater ratio in arm length.

(10) The springs 80, 82 (FIG. 1). The springs 80, 82 return the piston74 to its quiescent position after a deactivation of the solenoid 62.The springs 80, 82 are at the fulcrum 72 of the lever arm 84.

(11) Passivation layers (not shown). All surfaces are preferably coatedwith passivation layers, which may be silicon nitride (Si₃N₄), diamondlike carbon (DLC), or other chemically inert, highly impermeable layer.The passivation layers are especially important for device lifetime, asthe active device is immersed in the ink.

As will be evident from the foregoing description, there is an advantagein ejecting the drop on deactivation of the solenoid 62. This advantagecomes from the rate of acceleration of the moving magnetic pole 68.

The force produced by the moveable magnetic pole 68 by anelectromagnetically induced field is approximately proportional to theinverse square of the gap between the moveable and static magnetic poles68, 66. When the solenoid 62 is off, this gap is at a maximum. When thesolenoid 62 is turned on, the moveable pole 68 is attracted to thestatic pole 66. As the gap decreases, the force increases, acceleratingthe movable pole 68 faster. The velocity increases in a highlynon-linear fashion, approximately with the square of time. During thereverse movement of the moveable pole 68 upon deactivation, theacceleration of the moveable pole 68 is greatest at the beginning andthen slows as the spring elastic stress falls to zero. As a result, thevelocity of the moveable pole 68 is more uniform during the reversestroke movement.

(1) The velocity of the piston or plunger 74 is constant over theduration of the drop ejection stroke.

(2) The piston or plunger 74 can be entirely removed from the inkchamber 76 during the ink fill stage, and thereby the nozzle fillingtime can be reduced, allowing faster printhead operation.

However, this approach does have some disadvantages over a direct firingtype of actuator:

(1) The stresses on the spring 80, 82 are relatively large. Carefuldesign is required to ensure that the springs operate at below the yieldstrength of the materials used.

(2) The solenoid 62 must be provided with a “keeper” current for thenozzle fill duration. The keeper current will typically be less than 10%of the solenoid actuation current. However, the nozzle fill duration istypically around 50 times the drop firing duration, so the keeper energywill typically exceed the solenoid actuation energy.

(3) The operation of the actuator is more complex due to the requirementfor a “keeper” phase.

The printhead is fabricated from two silicon wafers. A first wafer isused to fabricate the print nozzles (the printhead wafer) and a secondwafer (the Ink Channel Wafer) is utilised to fabricate the various inkchannels in addition to providing a support means for the first channel.The fabrication process then proceeds as follows:

(1) Start with a single crystal silicon wafer 90, which has a buriedepitaxial layer 92 of silicon which is heavily doped with boron. Theboron should be doped to preferably 10²⁰ atoms per cm³ of boron or more,and be approximately 3 μm thick, and be doped in a manner suitable forthe active semiconductor device technology chosen. The wafer diameter ofthe printhead wafer should be the same as the ink channel wafer.

(2) Fabricate the drive transistors and data distribution circuitry 64according to the process chosen (eg. CMOS).

(3) Planarize the wafer 90 using chemical mechanical planarization(CMP).

(4) Deposit 5 mm of glass (SiO₂) over the second level metal.

(5) Using a dual damascene process, etch two levels into the top oxidelayer. Level 1 is 4 μm deep, and level 2 is 5 μm deep. Level 2 contactsthe second level metal. The masks for the static magnetic pole are used.

(6) Deposit 5 μm of nickel iron alloy (NiFe).

(7) Planarize the wafer using CMP, until the level of the SiO₂ isreached forming the magnetic pole 66.

(8) Deposit 0.1 μm of silicon nitride (Si₃N₄).

(9) Etch the Si₃N₄ for via holes for the connections to the solenoids,and for the nozzle chamber region 76.

(10) Deposit 4 μm of SiO₂.

(11) Plasma etch the SiO₂ in using the solenoid and support post mask.

(12) Deposit a thin diffusion barrier, such as Ti, TiN, or TiW, and anadhesion layer if the diffusion layer chosen has insufficient adhesion.

(13) Deposit 4 μm of copper for forming the solenoid 62 and spring posts94. The deposition may be by sputtering, CVD, or electroless plating. Aswell as lower resistivity than aluminium, copper has significantlyhigher resistance to electro-migration. The electro-migration resistanceis significant, as current densities in the order of 3×10⁶ Amps/cm² maybe required. Copper films deposited by low energy kinetic ion biassputtering have been found to have 1,000 to 100,000 times largerelectro-migration lifetimes larger than aluminium silicon alloy. Thedeposited copper should be alloyed and layered for maximumelectro-migration lifetimes than aluminium silicon alloy. The depositedcopper should be alloyed and layered for maximum electro-migrationresistance, while maintaining high electrical conductivity.

(14) Planarize the wafer using CMP, until the level of the SiO₂ isreached. A damascene process is used for the copper layer due to thedifficulty involved in etching copper. However, since the damascenedielectric layer is subsequently removed, processing is actually simplerif a standard deposit/etch cycle is used instead of damascene. However,it should be noted that the aspect ratio of the copper etch would be 8:1for this design, compared to only 4:1 for a damascene oxide etch. Thisdifference occurs because the copper is 1 μm wide and 4 μm thick, buthas only 0.5 μm spacing. Damascene processing also reduces thelithographic difficultly, as the resist is on oxide, not metal.

(15) Plasma etch the nozzle chamber 76, stopping at the boron dopedepitaxial silicon layer 92. This etch will be through around 13 μm ofSiO₂, and 8 μm of silicon. The etch should be highly anisotropic, withnear vertical sidewalls. The etch stop detection can be on boron in theexhaust gasses. If this etch is selective against NiFe, the masks forthis step and the following step can be combined, and the following stepcan be eliminated. This step also etches the edge of the printhead waferdown to the boron layer, for later separation.

(16) Etch the SiO₂ layer. This need only be removed in the regions abovethe NiFe fixed magnetic poles, so it can be removed in the previous stepif an Si and SiO₂ etch selective against NiFe is used.

(17) Conformably deposit 0.5 μm of high density Si₃N₄. This forms acorrosion barrier, so should be free of pinholes, and be impermeable toOH ions.

(18) Deposit a thick sacrificial layer. This layer should entirely fillthe nozzle chambers, and coat the entire wafer to an added thickness of8 μm. The sacrificial layer may be SiO₂.

(19) Etch two depths in the sacrificial layer for a dual damasceneprocess. The deep etch is 8 μm, and the shallow etch is 3 μm. The masksdefine the piston 74, the lever arm 84, the springs 80, 82 and themoveable magnetic pole 68.

(20) Conformably deposit 0.1 μm of high density Si₃N₄. This forms acorrosion barrier, so should be free of pinholes, and be impermeable toOH ions.

(21) Deposit 8 μm of nickel iron alloy (NiFe).

(22) Planarize the wafer using CMP, until the level of the SiO₂ isreached.

(23) Deposit 0.1 μm of silicon nitride (Si₃N₄).

(24) Etch the Si₃N₄ everywhere except the top of the plungers.

(25) Open the bond pads.

(26) Permanently bond the wafer onto a pre-fabricated ink channel wafer.The active side of the printhead wafer faces the ink channel wafer. Theink channel wafer is attached to a backing plate, as it has already beenetched into separate ink channel chips.

(27) Etch the printhead wafer to entirely remove the backside silicon tothe level of the boron doped epitaxial layer 92. This etch can be abatch wet etch in ethylenediamine pyrocatechol (EDP).

(28) Mask a nozzle rim 96 from the underside of the printhead wafer.This mask also includes the chip edges.

(31) Etch through the boron doped silicon layer 92, thereby creating thenozzle holes 70. This etch should also etch fairly deeply into thesacrificial material in the nozzle chambers 76 to reduce time requiredto remove the sacrificial layer.

(32) Completely etch the sacrificial material. If this material is SiO₂then a HF etch can be used. The nitride coating on the various layersprotects the other glass dielectric layers and other materials in thedevice from HF etching. Access of the HF to the sacrificial layermaterial is through the nozzle, and simultaneously through the inkchannel chip. The effective depth of the etch is 21 μm.

(33) Separate the chips from the backing plate. Each chip is now a fullprinthead including ink channels. The two wafers have already beenetched through, so the printheads do not need to be diced.

(34) Test the printheads and TAB bond the good printheads.

(35) Hydrophobize the front surface of the printheads.

(36) Perform final testing on the TAB bonded printheads.

FIG. 17 shows a perspective view, in part in section, of a single inkjet nozzle arrangement 60 constructed in accordance with the preferredembodiment.

One alternative form of detailed manufacturing process which can be usedto fabricate monolithic ink jet printheads operating in accordance withthe principles taught by the present embodiment can proceed utilizingthe following steps:

1. Using a double-sided polished wafer 90 deposit 3 microns of epitaxialsilicon 92 heavily doped with boron.

2. Deposit 10 microns of epitaxial silicon 98, either p-type or n-type,depending upon the CMOS process used.

3. Complete a 0.5-micron, one poly, 2 metal CMOS process. This step isshown in FIG. 19. For clarity, these diagrams may not be to scale, andmay not represent a cross section though any single plane of the nozzle.FIG. 18 is a key to representations of various materials in thesemanufacturing diagrams.

4. Etch the CMOS oxide layers down to silicon or aluminum using Mask 1.This mask defines the nozzle chamber 76, the edges of the printheadschips, and the vias for the contacts from the aluminum electrodes to twohalves of the fixed magnetic pole 66.

5. Plasma etch the silicon 90 down to the boron doped buried layer 92,using oxide from step 4 as a mask. This etch does not substantially etchthe aluminum. This step is shown in FIG. 20.

6. Deposit a seed layer of cobalt nickel iron alloy. CoNiFe is chosendue to a high saturation flux density of 2 Tesla, and a low coercivity.[Osaka, Tetsuya et al, A soft magnetic CoNiFe film with high saturationmagnetic flux density, Nature 392, 796-798 (1998)].

7. Spin on 4 microns of resist 99, expose with Mask 2, and develop. Thismask defines the fixed magnetic pole 66 and the nozzle chamber wall, forwhich the resist 99 acts as an electroplating mold. This step is shownin FIG. 21.

8. Electroplate 3 microns of CoNiFe 100. This step is shown in FIG. 22.

9. Strip the resist and etch the exposed seed layer. This step is shownin FIG. 23.

10. Deposit 0.1 microns of silicon nitride (Si3N4).

11. Etch the nitride layer using Mask 3. This mask defines the contactvias from each end of the solenoid 62 to the two halves of the fixedmagnetic pole 66.

12. Deposit a seed layer of copper. Copper is used for its lowresistivity (which results in higher efficiency) and its highelectromigration resistance, which increases reliability at high currentdensities.

13. Spin on 5 microns of resist 101, expose with Mask 4, and develop.This mask defines a spiral coil for the solenoid 62, the nozzle chamberwall and the spring posts 94, for which the resist acts as anelectroplating mold. This step is shown in FIG. 24.

14. Electroplate 4 microns of copper 103.

15. Strip the resist 101 and etch the exposed copper seed layer. Thisstep is shown in FIG. 25.

16. Wafer probe. All electrical connections are complete at this point,bond pads are accessible, and the chips are not yet separated.

17. Deposit 0.1 microns of silicon nitride.

18. Deposit 1 micron of sacrificial material 102. This layer determinesthe magnetic gap 114.

19. Etch the sacrificial material 102 using Mask 5. This mask definesthe spring posts 94 and the nozzle chamber wall. This step is shown inFIG. 26.

20. Deposit a seed layer of CoNiFe.

21. Spin on 4.5 microns of resist 104, expose with Mask 6, and develop.This mask defines the walls of the magnetic plunger or piston 74, thelever arm 84, the nozzle chamber wall and the spring posts 94. Theresist forms an electroplating mold for these parts. This step is shownin FIG. 27.

22. Electroplate 4 microns of CoNiFe 106. This step is shown in FIG. 13.

23. Deposit a seed layer of CoNiFe.

24. Spin on 4 microns of resist 108, expose with Mask 7, and develop.This mask defines the roof of the magnetic plunger 74, the nozzlechamber wall, the lever arm 84, the springs 80, 82, and the spring posts94. The resist 108 forms an electroplating mold for these parts. Thisstep is shown in FIG. 29.

25. Electroplate 3 microns of CoNiFe 110. This step is shown in FIG. 30.

26. Mount the wafer 90 on a glass blank 112 and back-etch the wafer 90using KOH, with no mask. This etch thins the wafer 90 and stops at theburied boron doped silicon layer 92. This step is shown in FIG. 31.

27. Plasma back-etch the boron doped silicon layer 92 to a depth of 1micron using Mask 8. This mask defines the nozzle rim 96. This step isshown in FIG. 32.

28. Plasma back-etch through the boron doped layer 92 using Mask 9. Thismask defines the ink ejection port 78, and the edge of the chips. Atthis stage, the chips are separate, but are still mounted on the glassblank 112. This step is shown in FIG. 33.

29. Detach the chips from the glass blank 112. Strip all adhesive,resist, sacrificial, and exposed seed layers. This step is shown in FIG.34.

30. Mount the printheads in their packaging, which may be a moldedplastic former incorporating ink channels which supply different colorsof ink to the appropriate regions of the front surface of the wafer.

31. Connect the printheads to their interconnect systems.

32. Hydrophobize the front surface of the printheads.

33. Fill the completed printheads with ink and test them. A fillednozzle is shown in FIG. 35.

The following description is of an embodiment of the invention coveredby U.S. patent application Ser. No. 09/113,061 to the applicant. In thisembodiment, a linear stepper motor is utilised to control a plungerdevice. The plunger device compresses ink within a nozzle chamber tocause the ejection of ink from the chamber on demand.

Turning to FIG. 36, there is illustrated a single nozzle arrangement 120as constructed in accordance with this embodiment. The nozzlearrangement 120 includes a nozzle chamber 122 into which ink flows via anozzle chamber filter portion 124 which includes a series of posts whichfilter out foreign bodies in the ink inflow. The nozzle chamber 122includes an ink ejection port 126 for the ejection of ink on demand.Normally, the nozzle chamber 122 is filled with ink.

A linear actuator 128 is provided for rapidly compressing a nickelferrous plunger 130 into the nozzle chamber 122 so as to compress thevolume of ink within the chamber 122 to thereby cause ejection of dropsfrom the ink ejection port 126. The plunger 130 is connected to astepper moving pole device 132 of the linear actuator 128 which isactuated by means of a three phase arrangement of electromagnets 134,136, 138, 140, 142, 144, 146, 148, 150, 152, 154, 156. Theelectromagnets are driven in three phases with electro magnets 134, 146,140 and 152 being driven in a first phase, electromagnets 136, 148, 142,154 being driven in a second phase and electromagnets 138, 150, 144, 156being driven in a third phase. The electromagnets are driven in areversible manner so as to de-actuate the plunger 130 via actuator 128.The actuator 128 is guided at one end by a means of a guide 158, 160. Atthe other end, the plunger 130 is coated with a hydrophobic materialsuch as polytetrafluoroethylene (PTFE) which can form a major part ofthe plunger 130. The PTFE acts to repel the ink from the nozzle chamber122 resulting in the creation of menisci 224, 226 (FIG. 59( a)) betweenthe plunger 130 and side walls 162, 164. The surface tensioncharacteristics of the menisci 224, 226 act to guide the plunger 130within the nozzle chamber 122. The menisci 224, 226 further stop inkfrom flowing out of the chamber 122 and hence the electromagnets 134 to156 can be operated in the atmosphere.

The nozzle arrangement 120 is therefore operated to eject drops ondemand by means of activating the actuator 128 by appropriatelysynchronised driving of electromagnets 134 to 156. The actuation of theactuator 128 results in the plunger 130 moving towards the nozzle inkejection port 126 thereby causing ink to be ejected from the port 126.

Subsequently, the electromagnets 134 to 156 are driven in reversethereby moving the plunger 130 in an opposite direction resulting in theinflow of ink from an ink supply connected to an ink inlet port 166.

Preferably, multiple ink nozzle arrangements 120 can be constructedadjacent to one another to form a multiple nozzle ink ejectionmechanism. The nozzle arrangements 120 are preferably constructed in anarray print head constructed on a single silicon wafer which issubsequently diced in accordance with requirements. The diced printheads can then be interconnected to an ink supply which can comprise athrough chip ink flow or ink flow from the side of a chip.

Turning now to FIG. 37, there is shown an exploded perspective of thevarious layers of the nozzle arrangement 120. The nozzle arrangement 120can be constructed on top of a silicon wafer 168 which has a standardelectronic circuitry layer such as a two level metal CMOS layer 170. Thetwo metal CMOS layer 170 provides the drive and control circuitry forthe ejection of ink from the nozzles 120 by interconnection of theelectromagnets to the CMOS layer 170. On top of the CMOS layer 170 is anitride passivation layer 172 which passivates the lower layers againstany ink erosion in addition to any etching of the lower CMOS glass layer170 should a sacrificial etching process be used in the construction ofthe nozzle arrangement 120.

On top of the nitride layer 172 are constructed various other layers.The wafer layer 168, the CMOS layer 170 and the nitride passivationlayer 172 are constructed with the appropriate vias for interconnectionwith the above layers. On top of the nitride layer 172 is constructed abottom copper layer 174 which interconnects with the CMOS layer 170 asappropriate. Next, a nickel ferrous layer 176 is constructed whichincludes portions for the core of the electromagnets 134 to 156 and theactuator 128 and guides 158, 160. On top of the NiFe layer 176 isconstructed a second copper layer 178 which forms the rest of theelectromagnetic device. The copper layer 178 can be constructed using adual damascene process. Next, a PTFE layer 180 is laid down followed bya nitride layer 182 which defines the side filter portions 124 and sidewall portions 162, 164 of the nozzle chamber 122. The ejection port 126and a nozzle rim 184 are etched into the nitride layer 182. A number ofapertures 186 are defined in the nitride layer 182 to facilitate etchingaway any sacrificial material used in the construction of the variouslower layers including the nitride layer 182.

It will be understood by those skilled in the art of construction ofmicro-electro-mechanical systems (MEMS) that the various layers 170 to182 can be constructed using a sacrificial material to support thelayers. The sacrificial material is then etched away to release thecomponents of the nozzle arrangement 120.

For a general introduction to a micro-electro mechanical system (MEMS)reference is made to standard proceedings in this field including theproceedings of the SPIE (International Society for Optical Engineering),volumes 2642 and 2882 which contain the proceedings for recent advancesand conferences in this field.

One form of detailed manufacturing process which can be used tofabricate monolithic ink jet print heads operating in accordance withthe principles taught by the present embodiment can proceed utilizingthe following steps:

1. Using a double sided polished wafer 188, complete drive transistors,data distribution, and timing circuits using a 0.5 micron, one poly, 2metal CMOS process. This step is shown in FIG. 39. For clarity, thesediagrams may not be to scale, and may not represent a cross sectionthough any single plane of the nozzle 120. FIG. 38 is a key torepresentations of various materials in these manufacturing diagrams,and those of other cross-referenced ink jet configurations.

2. Deposit 1 micron of sacrificial material 190.

3. Etch the sacrificial material 190 and the CMOS oxide layers down tosecond level metal using Mask 1. This mask defines contact vias 192 fromthe second level metal electrodes to the solenoids. This step is shownin FIG. 40.

4. Deposit a barrier layer of titanium nitride (TiN) and a seed layer ofcopper.

5. Spin on 2 microns of resist 194, expose with Mask 2, and develop.This mask defines the lower side of a solenoid square helix. The resist194 acts as an electroplating mold. This step is shown in FIG. 41.

6. Electroplate 1 micron of copper 196. Copper is used for its lowresistivity (which results in higher efficiency) and its highelectromigration resistance, which increases reliability at high currentdensities.

7. Strip the resist 198 and etch the exposed barrier and seed layers.This step is shown in FIG. 42.

8. Deposit 0.1 microns of silicon nitride.

9. Deposit a seed layer of cobalt nickel iron alloy. CoNiFe is chosendue to a high saturation flux density of 2 Tesla, and a low coercivity.[Osaka, Tetsuya et al, A soft magnetic CoNiFe film with high saturationmagnetic flux density, Nature 392, 796-798 (1998)].

10. Spin on 3 microns of resist 198, expose with Mask 3, and develop.This mask defines all of the soft magnetic parts, being the fixedmagnetic pole of the electromagnets, 134 to 156, the moving poles of thelinear actuator 128, the horizontal guides 158, 160, and the core of theink plunger 130. The resist 198 acts as an electroplating mold. Thisstep is shown in FIG. 43.

11. Electroplate 2 microns of CoNiFe 200. This step is shown in FIG. 44.

12. Strip the resist 198 and etch the exposed seed layer. This step isshown in FIG. 45.

13. Deposit 0.1 microns of silicon nitride (Si3N4) (not shown).

14. Spin on 2 microns of resist 202, expose with Mask 4, and develop.This mask defines solenoid vertical wire segments 204, for which theresist acts as an electroplating mold. This step is shown in FIG. 46.

15. Etch the nitride down to copper using the Mask 4 resist.

16. Electroplate 2 microns of copper 206. This step is shown in FIG. 47.

17. Deposit a seed layer of copper.

18. Spin on 2 microns of resist 208, expose with Mask 5, and develop.This mask defines the upper side of the solenoid square helix. Theresist 208 acts as an electroplating mold. This step is shown in FIG.48.

19. Electroplate 1 micron of copper 210. This step is shown in FIG. 49.

20. Strip the resist and etch the exposed copper seed layer, and stripthe newly exposed resist. This step is shown in FIG. 50.

21. Open the bond pads using Mask 6.

22. Wafer probe. All electrical connections are complete at this point,bond pads are accessible, and the chips are not yet separated.

23. Deposit 5 microns of PTFE 212.

24. Etch the PTFE 212 down to the sacrificial layer using Mask 7. Thismask defines the ink plunger 130. This step is shown in FIG. 51.

25. Deposit 8 microns of sacrificial material 214. Planarize using CMPto the top of the PTFE ink plunger 130. This step is shown in FIG. 52.

26. Deposit 0.5 microns of sacrificial material 216. This step is shownin FIG. 53.

27. Etch all layers of sacrificial material using Mask 8. This maskdefines the nozzle chamber walls 162, 164. This step is shown in FIG.54.

28. Deposit 3 microns of PECVD glass 218.

29. Etch to a depth of (approx.) 1 micron using Mask 9. This maskdefines the nozzle rim 184. This step is shown in FIG. 55.

30. Etch down to the sacrificial layer using Mask 10. This mask definesthe roof of the nozzle chamber 122, the ink ejection port 126, and thesacrificial etch access apertures 186. This step is shown in FIG. 56.

31. Back-etch completely through the silicon wafer (with, for example,an ASE Advanced Silicon Etcher from Surface Technology Systems) usingMask 11. Continue the back-etch through the CMOS glass layers until thesacrificial layer is reached. This mask defines ink inlets 220 which areetched through the wafer 168. The wafer 168 is also diced by this etch.This step is shown in FIG. 57.

32. Etch the sacrificial material away. The nozzle chambers 122 arecleared, the actuators 128 freed, and the chips are separated by thisetch. This step is shown in FIG. 58.

33. Mount the printheads in their packaging, which may be a moldedplastic former incorporating ink channels which supply the appropriatecolor ink to the ink inlets 220 at the back of the wafer. The packagealso includes a piezoelectric actuator attached to the rear of the inkchannels. The piezoelectric actuator provides the oscillating inkpressure required for the ink jet operation.

34. Connect the printheads to their interconnect systems. For a lowprofile connection with minimum disruption of airflow, TAB may be used.Wire bonding may also be used if the printer is to be operated withsufficient clearance to the paper.

35. Hydrophobize the front surface of the printheads.

36. Fill the completed printheads with ink 222 and test them. A fillednozzle is shown in FIG. 59.

IJ27 Printhead—U.S. Pat. No. 6,390,603

The following embodiment is referred to by the Applicant as the IJ27printhead. This printhead is described below with reference to FIGS. 60to 75, and in U.S. Pat. No. 6,390,603 the contents of which areincorporated by cross reference above. In the description of the IJ27embodiment, features and elements shown in FIGS. 60 to 75 are indicatedby the same reference numerals as those used to indicate the same orclosely corresponding features and elements of the embodiments shown inFIGS. 1 to 59.

In the IJ27 embodiment, a “roof shooting” ink jet printhead isconstructed utilizing a buckle plate actuator for the ejection of ink.In the preferred embodiment, the buckle plate actuator is constructedfrom polytetrafluoroethylene (PTFE) which provides superior thermalexpansion characteristics. The PTFE is heated by an integral, serpentineshaped heater, which preferably is constructed from a resistivematerial, such as copper.

Turning now to FIG. 60 there is shown a sectional perspective view of anink jet printhead 1 of the preferred embodiment. The ink jet printheadincludes a nozzle chamber 2 in which ink is stored to be ejected. Thechamber 2 can be independently connected to an ink supply (not shown)for the supply and refilling of the chamber. At the base of the chamber2 is a buckle plate 3 which comprises a heater element 4 which can be ofan electrically resistive material such as copper. The heater element 4is encased in a polytetrafluoroethylene layer 5. The utilization of thePTFE layer 5 allows for high rates of thermal expansion and thereforemore effective operation of the buckle plate 3. PTFE has a highcoefficient of thermal expansion (770×10⁻⁶) with the copper having amuch lower degree of thermal expansion. The copper heater element 4 istherefore fabricated in a serpentine pattern so as to allow theexpansion of the PTFE layer to proceed unhindered. The serpentinefabrication of the heater element 4 means that the two coefficients ofthermal expansion of the PTFE and the heater material need not beclosely matched. The PTFE is primarily chosen for its high thermalexpansion properties.

Current can be supplied to the buckle plate 3 by means of connectors 7,8 which inter-connect the buckle plate 3 with a lower drive circuitryand logic layer 26. Hence, to operate the ink jet head 1, the heatercoil 4 is energized thereby heating the PTFE 5. The PTFE 5 expands andbuckles between end portions 12, 13. The buckle causes initial ejectionof ink out of a nozzle 15 located at the top of the nozzle chamber 2.There is an air bubble between the buckle plate 3 and the adjacent wallof the chamber which forms due to the hydrophobic nature of the PTFE onthe back surface of the buckle plate 3. An air vent 17 connects the airbubble to the ambient air through a channel 18 formed between a nitridelayer 19 and an additional PTFE layer 20, separated by posts, e.g. 21,and through holes, e.g. 22, in the PTFE layer 20. The air vent 17 allowsthe buckle plate 3 to move without being held back by a reduction in airpressure as the buckle plate 3 expands. Subsequently, power is turnedoff to the buckle plate 3 resulting in a collapse of the buckle plateand the sucking back of some of the ejected ink. The forward motion ofthe ejected ink and the sucking back is resolved by an ink drop breakingoff from the main volume of ink and continuing onto a page. Ink refillis then achieved by surface tension effects across the nozzle part 15and a resultant inflow of ink into the nozzle chamber 2 through thegrilled supply channel 16.

Subsequently the nozzle chamber 2 is ready for refiring.

It has been found in simulations of the preferred embodiment that theutilization of the PTFE layer and serpentine heater arrangement allowsfor a substantial reduction in energy requirements of operation inaddition to a more compact design.

Turning now to FIG. 61, there is provided an exploded perspective viewpartly in section illustrating the construction of a single ink jetnozzle in accordance with the preferred embodiment. The nozzlearrangement 1 is fabricated on top of a silicon wafer 25. The nozzlearrangement 1 can be constructed on the silicon wafer 25 utilizingstandard semi-conductor processing techniques in addition to thosetechniques commonly used for the construction ofmicro-electro-mechanical systems (MEMS). For a general introduction to amicro-electro mechanical system (MEMS) reference is made to standardproceedings in this field including the proceedings of the SPIE(International Society for Optical Engineering), volumes 2642 and 2882which contain the proceedings for recent advances and conferences inthis field.

On top of the silicon layer 25 is deposited a two level CMOS circuitrylayer 26 which substantially comprises glass, in addition to the usualmetal layers. Next a nitride layer 19 is deposited to protect andpassivate the underlying layer 26. The nitride layer 19 also includesvias for the interconnection of the heater element 4 to the CMOS layer26. Next, a PTFE layer 20 is constructed having the aforementionedholes, e.g. 22, and posts, e.g. 21. The structure of the PTFE layer 20can be formed by first laying down a sacrificial glass layer (not shown)onto which the PTFE layer 20 is deposited. The PTFE layer 20 includesvarious features, for example, a lower ridge portion 27 in addition to ahole 28 which acts as a via for the subsequent material layers. Thebuckle plate 3 (FIG. 60) comprises a conductive layer 31 and a PTFElayer 32. A first, thicker PTFE layer is deposited onto a sacrificiallayer (not shown). Next, a conductive layer 31 is deposited includingcontacts 29, 30. The conductive layer 31 is then etched to form aserpentine pattern. Next, a thinner, second PTFE layer is deposited tocomplete the buckle plate 3 (FIG. 60) structure.

Finally, a nitride layer can be deposited to form the nozzle chamberproper. The nitride layer can be formed by first laying down asacrificial glass layer and etching this to form walls, e.g. 33, andgrilled portions, e.g. 34. Preferably, the mask utilized results in afirst anchor portion 35 which mates with the hole 28 in layer 20.Additionally, the bottom surface of the grill, for example 34 meets witha corresponding step 36 in the PTFE layer 32. Next, a top nitride layer37 can be formed having a number of holes, e.g. 38, and nozzle port 15around which a rim 39 can be etched through etching of the nitride layer37. Subsequently the various sacrificial layers can be etched away so asto release the structure of the thermal actuator and the air ventchannel 18 (FIG. 60).

One form of detailed manufacturing process which can be used tofabricate monolithic ink jet print heads operating in accordance withthe principles taught by the present embodiment can proceed utilizingthe following steps:

1. Using a double sided polished wafer 25, complete drive transistors,data distribution, and timing circuits 26 using a 0.5 micron, one poly,2 metal CMOS process. Relevant features of the wafer 25 at this step areshown in FIG. 63. For clarity, these diagrams may not be to scale, andmay not represent a cross section though any single plane of the nozzle.FIG. 62 is a key to representations of various materials in thesemanufacturing diagrams, and those of other cross referenced ink jetconfigurations.

2. Deposit 1 micron of low stress nitride 19. This acts as a barrier toprevent ink diffusion through the silicon dioxide of the chip surface.

3. Deposit 2 microns of sacrificial material 50 (e.g. polyimide).

4. Etch the sacrificial layer 50 using Mask 1. This mask defines thePTFE venting layer support pillars 21 and anchor point. This step isshown in FIG. 64.

5. Deposit 2 microns of PTFE 20.

6. Etch the PTFE 20 using Mask 2. This mask defines the edges of thePTFE venting layer 20, and the holes 22 in this layer 20. This step isshown in FIG. 65.

7. Deposit 3 microns of sacrificial material 51.

8. Etch the sacrificial layer 51 using Mask 3. This mask defines theanchor points 12, 13 at both ends of the buckle actuator. This step isshown in FIG. 66.

9. Deposit 1.5 microns of PTFE 31.

10. Deposit and pattern resist using Mask 4. This mask defines theheater 11.

11. Deposit 0.5 microns of gold (or other heater material with a lowYoung's modulus) and strip the resist. Steps 10 and 11 form a lift-offprocess. This step is shown in FIG. 67.

12. Deposit 0.5 microns of PTFE 32.

13. Etch the PTFE 32 down to the sacrificial layer 51 using Mask 5. Thismask defines the actuator paddle 3 and the bond pads. This step is shownin FIG. 68.

14. Wafer probe. All electrical connections are complete at this point,and the chips are not yet separated.

15. Plasma process the PTFE to make the top and side surfaces of thebuckle actuator hydrophilic. This allows the nozzle chamber 2 to fill bycapillarity.

16. Deposit 10 microns of sacrificial material 52.

17. Etch the sacrificial material 52 down to nitride 19 using Mask 6.This mask defines the nozzle chamber 2. This step is shown in FIG. 69.

18. Deposit 3 microns of PECVD glass 37. This step is shown in FIG. 70.

19. Etch to a depth of 1 micron using Mask 7. This mask defines thenozzle rim 39. This step is shown in FIG. 71.

20. Etch down to the sacrificial layer 52 using Mask 8. This maskdefines the nozzle 15 and the sacrificial etch access holes 38. Thisstep is shown in FIG. 72.

21. Back-etch completely through the silicon wafer 25 (with, forexample, an ASE Advanced Silicon Etcher from Surface Technology Systems)using Mask 9. This mask defines the ink inlets which are etched throughthe wafer 25. The wafer 25 is also diced by this etch. This step isshown in FIG. 73.

22. Back-etch the CMOS oxide layers 26 and subsequently depositednitride layers 19 and sacrificial layer 50 and 51 through to PTFE 20 and32 using the back-etched silicon as a mask.

23. Etch the sacrificial material 52. The nozzle chambers are cleared,the actuators freed, and the chips are separated by this etch. This stepis shown in FIG. 74.

24. Mount the printheads in their packaging, which may be a moldedplastic former incorporating ink channels which supply the appropriatecolor ink to the ink inlets at the back of the wafer.

25. Connect the printheads to their interconnect systems. For a lowprofile connection with minimum disruption of airflow, TAB may be used.Wire bonding may also be used if the printer is to be operated withsufficient clearance to the paper.

26. Hydrophobize the front surface of the printheads.

27. Fill the completed printheads with ink 54 and test them. A fillednozzle is shown in FIG. 75.

It will be appreciated by a person skilled in the art that numerousvariations and/or modifications may be made to the present invention asshown in the specific embodiment without departing from the spirit orscope of the invention as broadly described. The present embodiment is,therefore, to be considered in all respects to be illustrative and notrestrictive.

The presently disclosed ink jet printing technology is potentiallysuited to a wide range of printing systems including: color andmonochrome office printers, short run digital printers, high speeddigital printers, offset press supplemental printers, low cost scanningprinters, high speed pagewidth printers, notebook computers with inbuiltpagewidth printers, portable color and monochrome printers, color andmonochrome copiers, color and monochrome facsimile machines, combinedprinter, facsimile and copying machines, label printers, large formatplotters, photograph copiers, printers for digital photographic‘minilabs’, video printers, PHOTO CD (PHOTO CD is a registered trademarkof the Eastman Kodak Company) printers, portable printers for PDAs,wallpaper printers, indoor sign printers, billboard printers, fabricprinters, camera printers and fault tolerant commercial printer arrays.

Ink Jet Technologies

The embodiments of the invention use an ink jet printer type device. Ofcourse many different devices could be used. However presently popularink jet printing technologies are unlikely to be suitable.

The most significant problem with thermal ink jet is power consumption.This is approximately 100 times that required for high speed, and stemsfrom the energy-inefficient means of drop ejection. This involves therapid boiling of water to produce a vapor bubble which expels the ink.Water has a very high heat capacity, and must be superheated in thermalink jet applications. This leads to an efficiency of around 0.02%, fromelectricity input to drop momentum (and increased surface area) out.

The most significant problem with piezoelectric ink jet is size andcost. Piezoelectric crystals have a very small deflection at reasonabledrive voltages, and therefore require a large area for each nozzle.Also, each piezoelectric actuator must be connected to its drive circuiton a separate substrate. This is not a significant problem at thecurrent limit of around 300 nozzles per printhead, but is a majorimpediment to the fabrication of pagewidth printheads with 19,200nozzles.

Ideally, the ink jet technologies used meet the stringent requirementsof in-camera digital color printing and other high quality, high speed,low cost printing applications. To meet the requirements of digitalphotography, new ink jet technologies have been created. The targetfeatures include:

low power (less than 10 Watts)

high resolution capability (1,600 dpi or more)

photographic quality output

low manufacturing cost

small size (pagewidth times minimum cross section)

high speed (<2 seconds per page).

All of these features can be met or exceeded by the ink jet systemsdescribed above.

1. A printhead for an inkjet printer, the printhead comprising: an arrayof ink ejection devices, each ink ejection device having a chamber forholding a quantity of ink, the chamber being partially defined by atleast one sidewall, an inlet in fluid communication with the chamber, anactuator disposed in each of the chambers respectively, a nozzle influid communication with each of the chambers respectively, the nozzleis formed in a nozzle plate on the printhead exterior; wherein, theinlet defines a flow path into the chamber and has a series of columnsextending across the flow path.
 2. A printhead according to claim 1wherein the series of columns and the at least one sidewall areintegrally formed with the nozzle plate.
 3. A printhead according toclaim 1 wherein the actuator is configured to displace a surface withinthe chamber to eject ink from the nozzle.
 4. A printhead according toclaim 3 wherein the actuator has a heater element for displacing thesurface using thermal expansion.
 5. A printhead according to claim 3wherein the surface is positioned in the chamber such that it opposesthe nozzle and the flow path from the inlet feeds ink between the nozzleand the surface of the actuator.
 6. A printhead according to claim 5wherein the surface defines a wall of the chamber opposite the nozzle.7. A printhead according to claim 5 wherein the surface is formed frommaterial including polytetrafluoroethylene.
 8. A printhead according toclaim 5 wherein during use, the surface reduces the chamber volume toeject ink from the nozzle.
 9. A printhead according to claim 8 whereinduring use, the surface increases the chamber volume as the actuatorreturns to its quiescent position after ejecting ink in order to drawrefill ink through the barrier structure in the inlet.
 10. A printheadaccording to claim 9 wherein the surface has a quadrilateral geometryand is fixed at two opposing parallel sides such that the surfacebuckles into the chamber when during actuation, and flattens whenreturning to its quiescent state.
 11. A printhead according to claim 10wherein the heater element is a conductor with a serpentine geometryextending across most of the surface.
 12. A printhead according to claim11 wherein actuator defines a non-ink contacting side opposite thesurface wherein during use, an air space forms on the non-ink contactingside.
 13. A printhead according to claim 12 wherein the air space isvented to atmosphere.
 14. A printhead according to claim 13 wherein thenon-ink contacting side of the surface is hydrophobic for maintainingthe air space.
 15. A printhead according to claim 14 wherein the seriesof columns creates a flow restriction for the refill ink flow to damposcillations in ink in the chamber immediately after refill.
 16. Aprinthead according to claim 1 wherein the series of columns is a grillefor filtering contaminants out of the ink flow into the chamber.